As typical lighting devices for fluorescent lamps (usually referred to as fluorescent lights) used in general, there have conventionally been lighting devices for various fluorescent lamps such as those of the glow starter and rapid start types, which are also known as magnetic ballasts, or the inverter type, also known as an electronic ballast.
The inverter type fluorescent lamp lighting devices, which have rapidly been becoming widespread in recent years in particular, are devices which convert an AC into a DC and then cause an inverter circuit constituted by a transistor, a capacitor, a choke coil and the like to generate a high voltage at a high frequency (20 kHz to 100 kHz) near a resonance frequency.
The high voltage switches on the fluorescent lamp, and thereafter a current flowing through the fluorescent lamp stably lights the fluorescent lamp at a lower voltage.
This is superior to the conventional magnetic ballasts of the glow starter and rapid start types using choke coils in terms of such characteristics as lower power, higher efficiency, usability at both 50 Hz or 60 Hz, lower noise and indiscernibility of flicker.
These will now be explained with reference to the drawings.
FIG. 8(a) is a diagram illustrating an example of glow starter type ballasts, FIG. 8(b) is a diagram illustrating an example of rapid start type ballasts, and FIG. 8(c) is a diagram illustrating an example of inverter type ballasts.
The glow starter type ballast illustrated in FIG. 8(a), which is the most popular type, preheats electrodes (also referred to as filaments; the same hereinafter) of a fluorescent lamp with a starting device using a glow starter (G), so as to enable lighting in a few seconds after switching on.
The rapid start type ballast illustrated in FIG. 8(b), which is used in combination with a rapid start type lamp, is lit instantaneously and simultaneously with preheating when switched on.
On the other hand, the ballast of the inverter type lighting device illustrated in FIG. 8(c) converts an AC within the AC input voltage range of 85 to 450 V into a DC and then causes an integrated circuit to drive an LED lamp at a high frequency such as that mentioned above (e.g. see page 4 and FIG. 2 of Patent Literature 1).
While a choke coil L is inserted in series with the LED lamp in order to smooth the current flowing through the LED lamp in this case, an electrolytic capacitor (not depicted) is typically inserted in parallel with the LED lamp.
FIG. 9 is a diagram illustrating an example in which two fluorescent lamps are connected in series to a series rapid ballast.
This configuration, in which two fluorescent lamps are connected in series and lit by a single ballast, is simpler and less expensive than one using two single-lamp ballasts or a flickerless ballast.
When powered, the electrodes of each of fluorescent lamps A and B are preheated, and the secondary voltage does not shift to normal discharging but attains a weakly discharging state due to a starting capacitor having a high impedance. The lowered voltage at both ends of the starting capacitor caused by the weak discharge current is applied to the fluorescent lamp B, and starts to discharge the fluorescent lamp B.
When discharging occurs in both fluorescent lamps, the starting capacitor at the high impedance is placed into a substantially non-operating state, so that normal discharging is generated in both fluorescent lamps, and a lit state is maintained.
Thus discharging lamps one by one in such a series connection can light two fluorescent lamps in series at a relatively low secondary voltage, but is disadvantageous in that both of the fluorescent lamps fail to light when one of them is removed for power saving or has burnt out.